Modern vehicles use three-way catalysts (TWC) for exhaust after-treatment of gasoline engines. With tightening government regulations on automobile emissions, feedback control is used to adequately regulate the engine air-to-fuel ratio (AFR). Some vehicles have a universal exhaust gas oxygen (UEGO) sensor upstream of the TWC and a heated exhaust gas oxygen (HEGO) sensor downstream of the TWC to control the AFR near stoichiometry. This is achieved by regulated the AFR to a set-point around stoichiometry, which in turn is fine-tuned based on the deviation of a HEGO voltage from a pre-determined HEGO-voltage set-point.
However, the physical geometry and arrangement of engine cylinders creates a non-uniform, zoned exhaust flow condition in the exhaust system. Various faults, such as an AFR imbalance between cylinders, may exacerbate this non-uniform, zoned exhaust flow condition so that the UEGO sensor may not equally detect all of the cylinders. An AFR imbalance between cylinders occurs when the AFR in one or more cylinders is different than the other cylinders due to a cylinder-specific malfunction, such as an intake manifold leak at a particular cylinder, a fuel injector problem, an individual cylinder exhaust gas recirculation runner imbalance, or a fuel-flow delivery problem. The detection of a cylinder with an air-fuel mal-distribution would require a rather large imbalance. This can lead to significant feedgas emissions such as carbon monoxide (CO) or the oxides of nitrogen (NOx) passing directly to the tailpipe, as the biased air/fuel mixture is fed directly to the catalyst, overwhelming the oxygen-storage buffer that allows for short deviations from stoichiometry.
The inventors herein have recognized the above issues and have devised various approaches to solve them. In particular, systems and methods for identifying and mitigating air-fuel imbalance faults specific to an engine cylinder are provided. In one embodiment, a method comprises indicating a cylinder imbalance by comparing time-aligned readings from exhaust gas oxygen sensors, the exhaust gas oxygen sensors positioned symmetrically opposite each other within an exhaust passage downstream of a catalyst. In this way, an air-fuel imbalance fault may be accurately detected in a non-uniform exhaust flow. Mitigating actions can be taken once an air-fuel imbalance fault is detected, resulting in reduced tailpipe emissions.
In another embodiment, a method comprises: indicating a cylinder imbalance by comparing time-aligned readings from exhaust gas oxygen sensors, the exhaust gas oxygen sensors positioned symmetrically opposite each other within an exhaust passage downstream of a catalyst; and selecting one of the exhaust gas oxygen sensors to use for outer loop control. In this way, a rich or lean cylinder-specific air-fuel imbalance fault may be identified.
In another embodiment, a method comprises: indicating a cylinder imbalance by comparing time-aligned readings from exhaust gas oxygen sensors, the exhaust gas oxygen sensors positioned symmetrically opposite each other within an exhaust passage downstream of a catalyst; selecting one of the exhaust gas oxygen sensors for outer loop control; and adjusting fuel sequentially to individual cylinders to indicate which cylinder is imbalanced. In this way, a specific cylinder with an air-fuel imbalance fault may be identified and the fault mitigated such that tailpipe emissions are maintained within regulated levels.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.